Source of propagules of the fouling green macroalgae in the Subei Shoal,China

Since 2007,large-scale green tides dominated by Ulva prolifera consecutively bloomed in the Yellow Sea and caused great economic losses.The fouling U.prolifera on the Pyropia yezoensis aquaculture rafts in the Subei Shoal was regarded as the major source of the floating biomass.However,it was still unclear about the seed source of fouling green macroalgae attached on the rafts.In this study,the field surveys and the indoor experiments were conducted to reveal the source of propagules of the fouling green macroalgae on the rafts and to study the anti-fouling material for P.yezoensis aquaculture rafts which could possibly be a feasible strategy to control the green tides in the Yellow Sea.The results showed that（1） micro-propagules of several green macroalgal species,including U.prolifera,U.linza,U.compressa,U.flexuosa,and Blidingia sp.coexisted in the waters and sediments in the Subei Shoal and their proportion remarkably changed over time;（2） the bamboo poles with peeling treatment could significantly reduce the amount of U.prolifera micro-propagules attached.This study confirmed that the micro-propagules distributed in the Subei Shoal area were the precursors of the green tides,and provided a feasible method to control the Yellow Sea large-scale green tides at the beginning.

Responses of Bruguiera sexangula propagules to beneficial microbes in the nursery

Bruguiera sexangula （Lout） Poir., a threatened mangrove tree, was inoculated with beneficial microbes in a nursery to assess any improvements in growth and bio- mass. From soil samples from the rhizosphere of B. sexangula in a mangrove forest in Panangadu of Kerala India, nitrogen-fixing bacteria Azotobacter chroococcum and Azospirillum brasilense were isolated. The phosphatesolubilising bacterium Bacillus megaterium and potassiummobilizing bacteria Frateruria aurantia were also isolated and cultured on suitable media. Later, ripe propagules of B. sexangula were collected from matured trees and raised in sterilized soil bags （13 × 25 cm） containing sterilized soil and sand （2：1 ratio）. The cultured beneficial microbes were propagated and used to inoculate the ripe propagules of B. sexangula and maintained in the nursery for 6 months. After 6 months, growth and biomass of the inoculated propagules were greater than for the uninoculated control propagules. Shoot length, number of leaves, stem girth and root length were also significantly greater than in the controls. This study showed that the mangrove-specific beneficial microbes influenced the growth of B. sexangula

Germination and Photosynthetic Responses to Salinity and Alkalinity in Avicenna marina Propagules

Avicenna marina(Forssk.)Vierh is a halophytic mangrove.The reproductive unit is green and has photosynthetic propagules.Mangroves are naturally exposed to fluctuations in some abiotic factors at the soil surface,including salinity and alkalinity.The objective of this study was to determine the effects of two salts including NaCl and NaHCO_(3)on germination processes and discuss the relationships between cotyledon photosynthesis and embryo axis growth in A.marina propagules.These propagules came from Al Birk,located on the shoreline of the Saudi Red Sea.The results showed that the studied salts did not affect neither the final germination percentage nor the embryo axis growth.However,rooting and root growth were delayed by both salts at 300 mM and were strongly inhibited by 600 mM NaHCO_(3).Both NaCl and NaHCO_(3)reduced the photosynthetic activity.These two salts did not affect the other photosynthetic parameters,including stomatal conductance,net transpiration,and intercellular CO_(2).Thereafter,the reduction in net photosynthesis was not related to any limitation of stomatal conductance.The early germination phase was independent of cotyledon photosynthesis,whereas rooting and root growth may be limited by reduced photosynthesis under NaCl and NaHCO_(3).

Flocculation of Ulva microscopic propagules using modified clay:a mesocosm experiment

Microscopic propagules of Ulva species(UMPs)spread on Subei Shoal are believed to play a significant role in the formation of the Yellow Sea green tide.Previous laboratory and ship-based studies indicated that modified clay(MC)can effectively remove UMPs from the water column and restrict their germination.To evaluate the effectiveness of this method under natural conditions,a mesocosm experiment was conducted on the Zhugensha sandbank on Subei Shoal.The results show that the suspended particles on the sandbank would partially disturb the flocculation process between the MC and UMPs.However,the MC at a proper dose could effectively remove UMPs from the water column and decrease the adhesion and germination of UMPs on the nylon ropes that comprised the mariculture rafts by>75%.This method was proven a potential strategy to restrict the initial biomass accumulation of green algae on Subei Shoal.However,field trials in larger time-space scales are still needed to assess the efficiency of this method when used in the open sea.

Moss Propagules Banks in a Secondary Subtropical Moist Forest in Puerto Rico: A First Description

A bryophyte propagule bank serves as a source for population maintenance and survival, and many factors can influence these propagules’ germination. However, it is unknown how soil depths affect propagules banks, their diversity and abundance overtime in a Neotropical forest. To understand such a paradigm, soil samples were obtained from different depths (0 - 5 cm, 5 - 10 cm, and 10 - 15 cm) at Guajataca State Forest, Puerto Rico;then, they were transferred to the laboratory, cultured, and the amount of gametophytes from propagules present over a seven-month period were measured. Forest soil depth did affect the density of gametophytes. Gametophytes densities augmented overtime for almost all species. Two species mainly influenced the propagule production over time. Also, propagules can have a long-term germination potential for some species.

Nitrogen addition frequency and propagule pressure influence Solidago canadensis invasion into native plant community

Introduction:Propagule pressure(i.e.,the number of propagules)has long been recognized to play an essential role in plant invasion.But it is not clear whether propagule pressure influences the invasion of exotic plants into native plant communities when different frequencies of nitrogen are added.Method:We established an experiment with three plant communities that included native plant communities alone(four grasses,two legumes and two forbs)or native plant communities with one or five invasive plants,Solidago canadensis,under three frequencies of nitrogen addition(no addition or low or high addition with the same amount).Results:High propagule pressure significantly enhanced the biomass and relative dominance index of S.canadensis.Moreover,high propagule pressure only decreased the total and aboveground biomass of the legumes.However,the competitive effect between S.canadensis and the native community and biomass of the whole native community varied according to different frequencies.Conclusion:Overall,high propagule pressure encouraged invasion by S.canadensis,while alow nitrogen frequency was advantageous for the native community to resist invasion in this experiment.The results provide a scientific basis to manage and control the invasion of S.canadensis.

Bio-Morphological Characters of Alien Legume Species, Influencing Their Invasion in Natural Plant Communities

Five alien legume species, actively invading in natural plant communities in European part of Russia, were studied—Lupinus polyphyllus Lindl., Galega orientalis Lam., Robinia pseudoacacia L., Amorpha fruticosa L. and Caragana arborescens L. Distribution ranges (considering their invasive status) were mapped. Not a single bio-morphological character to forecast invasion success in natural plant communities within secondary distribution range was found. The data of key value/importance for explaining invasive success of the species studied were obtained. Two hypotheses— Propagule Pressure and Evolution of Invasiveness—were critically analyzed in view of the received data.

Germination Biology and Occurrence of Polyembryony in Two Forms of Cats Claw Creeper Vine, Dolichandra unguis-cati (Bignoniaceae): Implications for Its Invasiveness and Management

Cat’s claw creeper vine, Dolichandra unguis-cati (L.) Lohmann (syn. Macfadyena unguis-cati (L.) Gentry), is a major environmental weed in Australia. Two forms (“long” and “short” pod) of the weed occur in Australia. This investigation aimed to evaluate and compare germination behavior and occurrence of polyembryony (production of multiple seedlings from a single seed) in the two forms of the weed. Seeds were germinated in growth chambers set to 10/20°C, 15/25°C, 20/30°C, 30/45°C and 25°C, representing ambient temperature conditions of the region. Germination and polyembryony were monitored over a period of 12 weeks. For all the treatments in this study, seeds from the short pod form exhibited significantly higher germination rates and higher occurrence of polyembryony than those from the long pod form. Seeds from the long pod form did not germinate at the lowest temperature of 10/20°C;in contrast, those of the short pod form germinated under this condition, albeit at a lower rate. Results from this study could explain why the short pod form of D. unguis-cati is the more widely distributed form in Australia, while the long pod form is confined to a few localities. The results have implication in predicting future ranges of both forms of the invasive D. unguis-cati, as well as inform management decisions for control of the weed.

The environmental adaptability and reproductive properties of invasive green alga Codium fragile from the Nan'ao Island,South China Sea

It has been widely recognized that biological invasion has become one of the greatest threats to the ecosystem.Codium fragile is an invasive species which exhibits a variety of attributes like parthenogenesis,winter fragment,and vegetative reproduction;and therefore,it has become a successful invader,colonizing most subtropical regions.In China’s southeast coastal aquaculture waters,the green algal bloom caused by C.fragile will probably become a serious problem.In order to understand more details about the species,an experiment focused on its reproductive characteristics was conducted using culture established from a sample collected in the aquaculture raft of the Nan’ao Island in the South China Sea.The results showed that there were two types of gametes resembling aplanospores and zoospores respectively,both of which were able to germinate.During the gametes liberation,a long mucilage tube was formed out of the mouth of the gametangium assisting dispersal of gametes away from the parent plant.This tube was adapted not only to its surrounding flowing water environment but also to its parent plant’s outer gelatinous structure.In general,the optimum temperature for gametes release and germination was 15-20℃ and 15℃,respectively,which corresponded to the local offshore marine water.The plant was observed to produce vegetative buds under favourable reproductive conditions which were called propagules.They were capable of developing into filamentous thalli.The results will provide some scientific evidences for revealing the biological mechanism of bloom and control strategies of invasive green algae.

Understanding the Mechanism of Gamete Release in <i>Sargassum vulgare</i>C. Agardh

Sargassum vulgare C. Agardh shows androgynous receptacles, each bearing on an average 12 unisexual conceptacles which open outside by ostiole, and wherein gametangia (antheridia or oogonia) lie interspersed with paraphyses. Since out-put of eggs is extremely low, 4 - 6 per female conceptacle, Sargassum sp. ensures its survival under all eco-physiological conditions. The released oogonium is “wrapped” in sulphated polysaccharide-rich wall layer known to provide protection against desiccation. Oogonia after being “extruded” out of ostiole, are “incubated” on receptacle, where they grow into eggs that are easily contacted by spermatozoids. Gamete release is synchronous and almost simultaneous ensuring high rates of fertilization. The release occurs on days falling near a full moon or new moon, during low tides when conceptacles lie exposed. Gamete release occurs first from upper conceptacles, which “house” mature gametangia while lower ones are still developing. This results in gamete release over an extended period of time. The zygote dispersal and propagule recruitment also show adaptations selectively advantageous for the alga.

Inaccuracies in the history of a well-known introduction:a case study of the Australian House Sparrow(Passer domesticus)

Background:Modern ecosystems contain many invasive species as a result of the activity of acclimatisation societies that operated in the second half of the nineteenth century,and these species provide good opportunities for studying invasion biology.However,to gain insight into the ecological and genetic mechanisms that determine the rate of colonization and adaptation to new environments,we need a good understanding of the history of the introduced species,and a knowledge of the source population,timing,and number of individuals introduced is particularly important.However,any inaccuracies in the history of an introduction will affect subsequent assumptions and conclusions.Methods:Focusing on a single well-known species,the House Sparrow(Passer domesticus),we have documented the introduction into Australia using primary sources(e.g.acclimatisation records and newspaper articles).Results:Our revised history differs in a number of significant ways from previous accounts.Our evidence indicates that the House Sparrow was not solely introduced from source populations in England but also from Germany and most strikingly also from India—with the latter birds belonging to a different race.We also clarify the distinction between the number released and the number of founders,due to pre-release captive breeding programs,as well as identifying inaccuracies in a couple of well-cited sources with respect to the range expansion of the introduced populations.Conclusions:Our work suggests that caution is required for those studying introductions using the key sources of historical information and ideally should review original sources of information to verify the accuracy of published accounts.

Occurrence and distribution of arbuscular mycorrhizal fungi and microbial flora in the rhizosphere soils of mungbean [vigna radiata (L.) wilczek] and soybean [glycine max (L.) Merr.] from Adilabad, Nizamabad and Karimnagar districts of Andhra Pradesh state, India

Arbuscular Mycorrhizal (AM) fungi are key components of soil microbiota and obviously interact with other microorganisms in the rhizosphere which is the zone of influence of plant roots on microbial populations and other soil constituents. The microbial associates are more prone to general and annual fluctuations besides several abiotic factors such as environment and climatic factors which influence the whole process of AM - microbial interactions. Keeping in view, the importance of AM fungi the present study was undertaken for assessing the AM fungal spore population dynamics in the rhizosphere soil and its colonization, microbial (bacterial and fungal) population distribution in rhizosphere and nonrhizosphere soils as a function of seasonal variation in relation to soil physico-chemical factors associated with two legume crop plants collected from different districts of Andhra Pradesh state, India. AM fungal propagules and species were found to be well distributed varying in number from 12 to 89 spores per 10 gram soil in mungbean and 46 to 90 spores in soybean rhizosphere soils and percent root colonization in mungbean ranged from 36.74 to 90.68% however, in soybean it ranged from 23.58 to 76.92%. The 24 AM fungal species representing 4 genera were isolated, Glomus represented 12 spp. forming predominant genus. The Pearson Correlation coefficient data showed that the microbial population and AM fungal population and species, the degree of root colonization by native AM fungi varied significantly in two legume crop plants and influenced by soil edaphic factors. Significant negative correlation was recorded between root colonization and mean spore density of both the crops indicating that low levels of spore density are associated with high root colonization. The quantity and type of AM propagules also affected the dynamics of root colonization, which were also increased by increase in age of the crop plant.

Non-native plant species richness and influence of greenhouses and human populations in the conterminous United States

Background One issue in invasive plant ecology is identification of the factors related to the invasion process that increase number of non-native species.When invasion by non-native species increases,so does the probability that some non-native species will become harmful,or classified as invasive species,which disrupt natural ecosystems with attendant economic and social costs.I quantified patterns of how non-native species richness varied with vegetation types and human populations.To evaluate the relative importance of different predictor variables for invasion pathways in the conterminous United States,I modeled non-native plant species richness by county compared to current and historical human populations;greenhouses and nurseries;railroads,pipelines,transmission lines,and oil and gas wells;and land covers of impervious surface,development intensity categories,agriculture,and vegetation types.I also modeled these variables within vegetation types,excluding vegetation variables.Results To summarize patterns,non-native plant species richness increased from 72 to 200 with increasing human population density classes.Forests and forest land use mosaics had the greatest mean number of non-native plant species,ranging from 121 to 166,whereas grasslands and grassland mosaics had the least number of non-native plant species,about 70.For modeling variable importance,all combined variables had R^(2)values of 56%(random forests regressor)and 54%(cubist regressor)for predictions of withheld observations of non-native plant species rich-ness,with greenhouse density and percent forestlands as most influential variables.Single variables of greenhouses(R^(2)=29%),historical and current human populations(R^(2)=27%and 23%),impervious surface(25%),and medium intensity development(23%)were most associated with non-native plant species richness.For vegetation types,greenhouse and historical human population densities were influential variables particularly in forestlands,shrublands,and wetlands.Conclusions Based on these models,human population measures and horticultural locations of greenhouses and plant nurseries may have stronger relationships than measures of land use disturbance and transport with non-native plant species richness.

Water transfer determines the regional spread dynamics of non-native fish species

Interbasin water transfer projects(IBWT's)have emerged as dispersal corridors for aquatic species.However,little is known about how water transfer affects regional spread dynamics,or shapes the genetic diversity patterns of non-native populations.Shimofuri Goby Tridentiger bifasciatus is a globally introduced fish species with many wellestablished populations in IBWT's.Here,we used nuclear microsatellites to assess the genetic diversity and population structure of the Shimofuri Goby in its native and introduced sites belonging to two IBWT's in China.Our objectives were to(1)reveal the genetic diversity patterns of the Shimofuri Goby during regional spread,and(2)identify its mode of spreading in water transfer systems.We observed(1)a high level of genetic diversity in non-native populations without evidence of bottleneck effects,(2)that non-native populations with a longer water transfer times had a higher private allele richness,and(3)that non-native populations showed a highly mixed genetic structure,low level of genetic differentiation,and no significant relationship between geographical and genetic distances.Our results indicate that the genetic patterns of diversity of non-native populations are mainly shaped by a linear cascade spread processes due to long-distance movement of larvae,and are probably related to propagule pressure caused by the construction of water transfer.To manage the non-native populations of T.bifasciatus,preventive actions and physical removal should be implemented in IBWT's.

Are some communities of the coastal dune zonation more susceptible to alien plant invasion?

Aims Coastal areas,and in particular coastal dunes,are ecosystems strongly affected by the invasion of alien plants.However,few attempts have ever been made to quantify alien species incidence in different communities along the coastal zonation.This work aims to analyze the distribution of alien plants along the coastal zonation of sandy shores on the Tyrrhenian coast,addressing specifically differences among plant communities in abundance of alien plants.Methods The study was performed on recent dunes(Holocene)of the central western coast of Italy.We selected dune landscapes where invasion processes were particularly evident.Vegetation plots were randomly sampled and through cluster analysis,we identified six plant communities corresponding to the typical zonation described for the Tyrrhenian sandy coast of Central Italy.We evaluated and compared frequency and abundance of invasion in these different communities.Further,we investigated how propagule pressure(measured using as proxy human structures)contributed to the observed invasion patterns.Important Findings We found a relatively low total number of aliens but also a differential distribution pattern and strong abundance of some of the aliens in specific sectors of the vegetation zonation.The perennial community of transition dunes appears most affected by invasion processes,related almost exclusively to the frequent and widespread Carpobrotus aff.acinaciformis.This alien species reaches high cover values,apparently lowering cover of native species of transition dune plant communities.Higher levels of invasion in the transition dune can be partially explained because of greater propagule pressure in this section of the dune profile.Our findings thus have important conservation and management implications since transition dune communities with Crucianella maritima are rare and protected(sensu Habitat 92/43/EEC Directive)along the entire Italian coast.

Multiple mechanisms in woodland plant species invasion

Aims A plethora of theories explain species invasion,yet when tested in isolation,support or falsification becomes contingent on study species,system and approach.Our objective was to examine com-munity-level species invasion as a function of multiple competing hypotheses.Methods We used data from>3500 woodland plant species in 2750 plots in 49 national parks in eastern US deciduous forests to test multiple competing theories of species invasion:competition,empty niche,propagule pressure and latitude matching.We also tested interac-tions with residence time to account for non-native species naturali-zation and spread since arrival.Important Findings The non-native herbs generally thrived at latitudes similar to those from which they originated,but not necessarily where they were originally introduced to the eastern US.Overall,we found that each hypothesis explained at least some aspect of woodland plant species invasion,but examining them simultaneously allowed assessment of their relative strengths and interactions.Our results suggested that residence time is a strong predictor of non-native woodland plant success,particularly as it interacts with other mechanisms of inva-sion,such as competition(abundance of native woodland plants),climate matching(similar invaded latitude as home range),prop-agule pressure(distance to putative seed sources)and empty niche(relatedness to native plants).We found that initial barriers,such as distance from propagule source or suboptimal habitat,were over-come,as was resistance from native relatives.However,the biggest challenge for the non-native woodland plants appeared to be time,as they declined after~1 to 2 centuries.

Contributions of Trimorphic Life Cycles to Dispersal and Evolutionary Trends in Large Benthic Foraminifers

The basic life cycle of Foraminifera has long been recognized as alternation between sexual and asexual generations;a common modification is several successive asexual generations.Production and release of flagellated gametes also has been documented as the basic sexual-reproductive mode in extant lineages.Research on population dynamics,local spatial distributions,and biogeography of Amphistegina spp.and Heterostegina depressa have been augmented by culture studies over the past 50years,providing insights that have been widely used in paleoecological and paleoenvironmental interpretations.Hypotheses are proposed suggesting how stages in the life cycle might contribute to understanding biogeographic and evolutionary trends commonly observed in large benthic foraminifers.Recruitment of sexually-produced cryptobiotic propagules,followed by successive asexual generations(schizogeny),can potentially establish viable,locally-adapted populations within literally years,consistent with the concepts of both allopatric speciation and reticulate evolution associated with isolation and reconnection of local basins.The review concludes with the recommendation that future studies utilizing genomics,proteonomics,geochemistries,scanning technologies,and other approaches can promote greater understanding of both modern and fossil larger benthic foraminiferal lineages.

Modeling Responses of Leafy Spurge Dispersal to Control Strategies

Leafy spurge （Euphorbia esula L.） has substantial negative effects on grassland biodiversity, productivity, and economic benefit in North America. To predict these negative impacts, we need an appropriate plant-spread model which can simulate the response of an invading population to different control strategies. In this study, using a stochastic map lattice approach we generated a spatially explicitly stochastic process-based model to simulate dispersal trajectories of leafy spurge under various control scenarios. The model integrated dispersal curve, propagule pressure, and population growth of leafy spurge at local and short-temporal scales to capture spread features of leafy spurge at large spatial and long-temporal scales. Our results suggested that narrow-, medium-, and fat-tailed kernels did not differ in their ability to predict spread, in contrast to previous works. For all kernels, Allee effects were significantly present and could explain the lag phase （three decades） before leafy spurge spread accelerated. When simulating from the initial stage of introduction, Allee effects were critical in predicting spread rate of leafy spurge, because the prediction could be seriously affected by the low density period of leafy spurge community. No Allee effects models were not able to simulate spread rate well in this circumstance. When applying control strategies to the current distribution, Allee effects could stop the spread of leafy spurge; no Allee effects models, however, were able to slow but not stop the spread. The presence of Allee effects had significant ramifications on the efficiencies of control strategies. For both Allee and no Allee effects models, the later that control strategies were implemented, the more effort had to be input to achieve similar control results.

Human occupation explains species invasion better than biotic stability:evaluating Artocarpus heterophyllus Lam.(Moraceae;jackfruit)invasion in the Neotropics

Aims Biological invasions are recognized to put native species in risk of extinction.In this study,I tested whether the invasion of Artocarpus heterophyllus Lam.(Moraceae;jackfruit)in the Neotropics was explained by its biotic stability,an intrinsic force,or by human occupation,an extrinsic force.Methods I used an ensemble framework combining 12 ecological niche models(ENMs)and 4 atmosphere-ocean general circulation models.ENMs were constructed for the pre-industrial time period in the Indo-Malaya biogeographic region,the native habitat of A.heterophyllus,and were then projected to past(last glacial maximum,21000 years ago and mid-Holocene,6000 years ago)and future(end of century,2080)peri-ods.The ENMs were used to establish the biotic stability of A.hetero-phyllus in areas where it was predicted to be present concomitantly within these four time periods.This biotic stability was projected onto the Neotropics,and then I used a null model and logistic regression to test what the main driver of A.heterophyllus invasion.Important Findings In general,the presence of A.heterophyllus in the Neotropics was not explained by biotic stability,tested by the null model.However,human occupation explained much of its presence in the invaded habitat,once all standardized coefficients related to this driver was significant positive in the logistic regression.Based on these results,humans sustained the presence of A.het-erophyllus in the Neotropics,probably because of the additive influences of propagule pressure and habitat disturbance.Thus,the recommendation is that the cultivation of A.heterophyllus in the Neotropics must be regulated and supervised,primarily near reserve areas.

Departure from naturalized to invasive stage:a disturbanceinduced mechanism and associated interacting factors

Aims Within a habitat of multiple plant species,increased resource availabilities and altered species abundances following disturbances create opportunities for exotic species to successfully establish and subsequently naturalize into its non-native environment.Such post-disturbance changes in abiotic and biotic environments may also promote a naturalized exotic species(or invading species)to become invasive through rapid colonization of the habitat sites by reducing the extent and size of resident plant species.By combining species life history traits with that of the disturbance-induced changes in habitat characteristics,we aimed to determine those interacting factors and associated mechanism allowing an exotic invasion to start off.Methods We used a modified version of the classic competition–colonization(CC)model which was formulated first by Hastings(1980)and studied later by Tilman(1994)to explain spatial coexistence of multiple species.Within this model framework,recruitment-limited spatial competition has explicitly been linked with interspecific resource competition without altering the basic assumptions and structure of the original CC model.Important findings The model results showed that at a constant rate of resource supply,invading species can stably coexist with native species via trade-offs between species competitive ability and colonizing ability.On the other hand,the model predicted that with a fluctuating resource condition,invading species can successfully invade a habitat following continuous reductions in the size and extent of native species.Whether or not invading species holds competitive superiority over the native species for limiting resource,we showed that there exists a range of variation in available resource that allows an exotic invasion to start off in post-disturbance habitat.The associated disturbance-induced mechanism promoting invading species to become invasive has been identified.It states that occurrences of disturbances such as fire or clear-cutting influence variation in resource availability,and in addition open up many vacant microsites;given these disturbance-induced changes,invading species with a higher rate of propagule production and with a higher survival rate of adults particularly in low-resource condition recruits microsites at faster rate relative to native competitor species,and with a given range of variation in resource availabilities,it maintains continued expansions following reductions in size and extent of native species.Moreover,we identified those interacting factors and their specific roles that drive this mechanism.These factors include propagule supply,variable resource level and vacant microsite availability.Increased availability of vacant microsites following disturbances creates an opportunity for rapid colonization.Given this opportunity,higher number of propagules supplied by the invading species enhances the rate of colonization success,whereas the resource variation within a range of given thresholds maintains enhanced colonization rate of the invading species while it depresses native competitor species.Owing to the each factor’s invasion regulatory ability,controlling one or all of them may have strong negative impact on the occurrence of exotic invasion.